It is conventional in the manufacture of converters or converter devices to detect construction faults and/or component faults via unexpectedly quick heating of a converter phase using function tests or during final inspection or during subsequent runin inspection. For this purpose, a plurality of temperature sensors are generally provided in the converter, namely at least one sensor per phase and generally additionally a further temperature sensor which detects the overall temperature or housing temperature of the converter or converter device.
The multiple temperature information thus obtained can be used in the manufacture or else in the spot checking for the purpose of diagnostics in order to identify, for example, poor heat coupling to a heat sink in phase-specific fashion.
Secondly, it is also known to use DC/DC converters to transmit energy with a different DC output voltage, wherein in the simplest case, a switching device is provided which produces or interrupts a connection to a DC voltage source, with the duty factor of this switching device determining the level of the output voltage or the output current. In order to now achieve high powers, “multiphase” converters, namely converters with a plurality of units connected in parallel, are often used. These parallel units or phases are driven in phase-shifted fashion in order thus to enable a reduction or reduction in size of the required filter components.
In the case of such multiphase converters, the problem arises that, for example owing to component tolerances, an unbalanced load distribution, in particular current distribution (possibly also voltage distribution), can be provided on the individual phases even given the same pulse width of the PWM drive signal (PWM=pulse width modulation). However, this is undesirable since, firstly, the losses owing to the nonreactive resistance of the converter increase and thus the efficiency of the converter is impaired, and secondly, owing to an unevenly distributed current, for example, individual inductances enter saturation as a result of an excessively high phase current, which results in a reduction in the maximum power of the converter overall or in failure of one phase. Therefore, in practice, current balancing (generally: load balancing) is performed in the case of multiphase converter systems, for example, for which purpose conventional PWM closed-loop current control is provided. For example, the current of one phase is measured via a measuring resistor and calculated; the duty factors of the individual converter phases are in this case selected in such a way as to produce “balanced” (uniform) current splitting between the individual phases. This is realized by a corresponding adjustment of the respective phase duty factors, with it being possible for the individual duty factors to be completely different from one another. By virtue of balanced current splitting, both the influence of component tolerances and the effect of specific design imbalances in the construction of the converter, such as are caused by feed lines of different lengths to the respective phase, for example, can be reduced.